Fuel cells are electrochemical energy conversion devices which have been considered as an alternative for the conversion of energy to heat engines which are limited by their inherent thermodynamics. The concept of fuel cells has been generally known since the early 1960's when fuel cells were introduced as energy storage devices in the Gemini portion of the NASA space program.
A typical fuel cell consists of three components- two electrodes; that is, a cathodic element and an anodic element, and a bridging electrolyte which is sandwiched therebetween. Historically, fuel cells have been classified by means of the electrolyte utilized. To date, five classifications of fuel cells are known: Polymer Electrolyte Membrane (also referred to as Proton Exchange Membrane Fuel Cells (PEM), Alkaline Fuel Cells (AFC), Phosphoric Acid Fuel Cells (PAFC), Molten Carbonate Fuel Cells (MCFC), and Solid Oxide Fuel Cells (SOFC).
PEM-type fuel cells are particularly advantageous over the remaining types of fuel cells for various reasons. One advantage is the solid nature of the electrolyte used in the cell which minimizes the operational complications arising from the liquid electrolytes that are found in PAFCs and AFCs. Moreover, the nature of PEM-type fuel cells allow operation at relatively low temperatures (80 degrees C.) when compared to other fuel cell types, most particularly MCFCs and SOFCs which can only operate at much higher temperatures. In addition, PEM-type fuel cells are generally more efficient, have longer working lives and can maintain higher power densities than other forms of fuel cells.
PEM-type fuel cells, however, have not been commercially successful due to limitations found in currently known designs. The majority of these designs utilize flat plate geometries which are assembled in a parallel arrangement--the so-called "plate and frame" approach. These designs employ rather complex, and expensive "reactant flow plate" designs.
Another disadvantage of current "plate and frame" approaches is that these fuel cells assemblies must be manually manufactured by skilled artisans, making assembly expensive and time-consuming.
Still another disadvantage are the rigidity and bulkiness of the structures which are produced using "plate and frame" fuel cell designs. That is, in order to produce adequate power, a series of plates must be assembled together and then retained in a rigid and large enclosure. Such enclosures can not be retained easily in portable applications; for example, lap-top computers.
Finally, current fuel cell designs require thermal management for efficient operation. Although plate and frame designs for heat exchangers are commonly known, this type of fuel cell construction has a competing concern in that electrical and heat loads must be concurrently managed. The result is that often a separate cooling circuit is required, requiring additional cooling plates, making the design additionally bulky as well as expensive.
Presently known PEM-type fuel cells individually produce a small amount of voltage. To produce a significant amount of energy, the cells must be electrically connected in some manner. A disclosed way of electrically interconnecting fuel cells is described in U.S. Pat. No. 5,338,623 in which the fuel cells are stacked one upon another. Plate and frame approaches utilize a similar approach, making fuel cells of this type quite bulky. To date, known tubular fuel cell constructions, such as described in U.S. Pat. No. 5,336,570, are subject to large power losses due to the requirement of a large transverse sectional area which is wound on a substrate.
Finally, fuel cells in general utilize ion transfer through the membrane to produce desired electrochemical reactions. For these reactions to occur, reactants (usually hydrogen gas at the anode and oxygen from ambient air at the cathode) must be separately supplied from each electrode side of the membrane from an external source or tank.